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Fullerenes, Nanotubes and Carbon Nanostructures
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NEXAFS Spectra of Polymer-nanocarbon Composites
A. O. Pozdnyakovab; M. M. Brzhezinskayacd; A. S. Vinogradovc; K. Friedriche a Institute of Problems of Mechanical Engineering, St. Petersburg, Russian Federation b Ioffe PhysicoTechnical Institute, St. Petersburg, Russian Federation c V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg, Russian Federation d BESSY, Berlin, Germany e Institut für Verbundverkstoffe GmbH, Technisches Universität Kaiserslautern, Kaiserslautern, Germany Online publication date: 16 June 2010
To cite this Article Pozdnyakov, A. O. , Brzhezinskaya, M. M. , Vinogradov, A. S. and Friedrich, K.(2008) 'NEXAFS Spectra
of Polymer-nanocarbon Composites', Fullerenes, Nanotubes and Carbon Nanostructures, 16: 5, 471 — 474 To link to this Article: DOI: 10.1080/15363830802282409 URL: http://dx.doi.org/10.1080/15363830802282409
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Fullerenes, Nanotubes and Carbon Nanostructures, 16: 471–474, 2008 Copyright # Taylor & Francis Group, LLC ISSN 1536-383X print/1536-4046 online DOI: 10.1080/15363830802282409
NEXAFS Spectra of Polymer-nanocarbon Composites
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A. O. Pozdnyakov,1,2 M. M. Brzhezinskaya,3,4 A. S. Vinogradov,3 and K. Friedrich5 1
Institute of Problems of Mechanical Engineering, St. Petersburg, Russian Federation 2 Ioffe Physico-Technical Institute, St. Petersburg, Russian Federation 3 V.A. Fock Institute of Physics, St. Petersburg State University, St. Petersburg, Russian Federation 4 BESSY, Berlin, Germany 5 Institut fu¨r Verbundverkstoffe GmbH, Technisches Universita¨t Kaiserslautern, Kaiserslautern, Germany
Abstract: The near edge X-ray absorption fine structure (NEXAFS) spectra of polymethylmetacrylate (PMMA)-fullerene (Fu) C60 and PMMA-multiwall nanotubes (MWNT) composites treated at different temperatures are compared to the thermal desorption (TD) mass-spectrometric (MS) spectra. Keywords: Polymer composite, Fullerene, MWNT, NEXAFS, Thermal desorption, Spectra, Mass-spectrometry
INTRODUCTION The mechanisms controlling the extent of interaction in the polymernanocarbon composites are not yet well understood. Earlier TDMS studies showed (1) that in PMMA-C60 composites one can expect the presence of certain interaction between the components. In this study we inspect the electronic subsystem of this composite using the NEXAFS technique.
Address correspondence to A. O. Pozdnyakov, Institute of Problems of Mechanical Engineering, 199178, Bol’shoi pr. 61, V/O, St. Petersburg, Russian Federation. E-mail:
[email protected] 471
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EXPERIMENT We used PMMA Fluka, Mw5500000; fullerene C60, Aldrich, sublimed, 99.9%; toluene, Sigma-Aldrich, Chromasolv plus, for HPLC 99.9%; MWNT, Arkema. PMMA-C60 and PMMA-MWNT suspensions were prepared by co-dissolution of the polymer and C60 or MWNT solutions in toluene. The rated volume fractions of C60 and MWNT in dry polymer were , 0.1 and 0.3, respectively. The dried coatings were cast at stainless steel substrates. NEXAFS measurements were performed with the use of synchrotron radiation at the Russian-German beamline (RGL) at the BESSY II (Berlin, Germany). The NEXAFS spectra were obtained in the total electron yield (TEY) mode by detecting a sample current. The photon-energy resolution was set to 0.15 eV at the C1s edge (,285 eV). The details of the experiments as well as additional results on polystyrene and polyimide- C60 composites can be found elsewhere (2). TD-MS measurements were performed on as-prepared polymer films at the heating rate of ,8k/sec with the aid of time-of-flight mass spectrometer (1).
RESULTS AND DISCUSSION Figure 1 shows the C1s NEXAFS spectra for neat C60, PMMA and PMMA-C60 composite formed in different heat treatment conditions in air. The position of the lowest unoccupied orbitals (LUMOs) of neat C60 are in a good agreement with the literature (3). The spectra of the composite samples also contain the LUMOs of C60. Notable is the change in the relative intensity of LUMO and LUMO+1 upon heating the composite and the decrease in the relative intensity of the peaks characteristic of PMMA matrix on prolonged heating at 180uC. The heat treatment in the latter conditions leads to the visual change in color of the composite sample, probably pointing to certain degradation of the material. This treatment does not lead to the significant change in LUMO’s position and shape for C60 in the composite compared to those of neat C60. Further, as is seen from Figure 2 the TD-MS spectra of neat PMMA and PMMA-C60 are almost coinciding in the broad temperature range. However, certain differences are observed between the initial stages of TD spectra. These observations suggest that certain interactions between PMMA and C60 are already formed at fairly low temperatures. More research is underway to make deeper insight in this question. Figure 3 presents the NEXAFS spectra of MWNT and PMMAMWNT composite. MWNT spectra are fairly reliable (4). The spectral feature shown with the arrow may be attributed to the presence of carbon oxides at the MWNT. The analysis of the spectra shows that an interaction between the matrix and MWNT probably also exists. The
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NEXAFS Spectra of Polymer-nanocarbon Composites
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Figure 1. C1s NEXAFS spectra of C60 powder (dotted lines), PMMA after heating in air at 80uC for , 1 hour (1), PMMA-C60 composite after heating: in air at 80uC during several minutes (2), at 180uC for several minutes (3), at 180uC for , 1 hour (4).
Figure 2. TD spectra of PMMA (solid diamonds) and PMMA-C60 composite (open diamonds). The thin line shows the fit of the TD spectrum for PMMA by the solution of the first order kinetic equation with the activation energy , 155 kJ/mole (1).
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Figure 3. C1s NEXAFS spectra of MWNT (1) and PMMA-MWNT composite (2).
interaction is responsible for p states of the graphene wall of the nanotube. This fact is a matter of further studies. ACKNOWLEDGMENTS This work was supported by the bilateral Russian/Germany Program ‘‘RGL at BESSY.’’ A.O. Pozdnyakov expresses gratitude to RAS for supporting his participation in the program ‘‘New Materials and Structures,’’ Alexander von Humboldt Foundation for supporting his research during his stay at IVW, Technical University of Kaiserslautern, and ‘‘RGL at BESSY’’ for support of the project. M.M. Brzhezinskaya and A.S.Vinogradov acknowledge the Russian foundation for basic research (Grant 06-02-16998). REFERENCES 1. Pozdnyakov, A.O. (2007) Mass spectrometric research of polymer-fullerene composites In Fullerene Research Advances; Kramer, C.N. (ed.), Nova Science Pub. Inc.: New York, NY, USA, pp. 89–105. 2. Pozdnyakov, A.O., Brzhezinskaya, M.M., Zverev, D.A., Baitinger, E.M., Vinogradov, A.S., and Friedrich, K. (2005) BESSY Annual Report, Berliner Elektronenspeicherring–Gesellschaft fu¨r Synchrotronstrahlung m.b.lt. (BESSY), Berlin, Germany, pp. 308–310. 3. Guo, J.-H., Glans, P., Skytt, P., et al. (1995) Resonant excitation x-ray fluorescence from C60. Phys. Rev., B, 52(15): 10681. 4. Brzhezinskaya, M.M. and Baitinger, E.M. (2006) Plasmons in carbon nanotubes. In Trends in Nanotubes Research; Martin, D.A. (ed.), Nova Science Pub. Inc.: New York, NY, USA, 235–275.
